Polymer solar cells (PSCs) have attracted great attention due to their potential applications as low-cost renewable energy sources. In Conventional PSCs, anode degradation caused by the PEDOT diffusion induced etching of ITO can occur in conventional PSCs, resulting in short lifetimes of the device. In order to enhance the stability of PSCs, PSCs of inverted structures, where the nature of charge collection is reversed, have been employed as an alternative to improve the lifetime of solar cells. To further enhance the device stability, inorganic semiconductor oxides inserted between ITO and the active layer has been implemented as a buffer layer in an inverted device structure to selectively collect electrons as well as avoid the contact of ITO film with PEDOT polymer. The buffer layer works as an electron-collecting electrode and a hole-blocking layer, which is essential for achieving high efficiency PSCs.
SrTiO3 with the perovskite structure is a very attractive material for application in microelectronics due to its high charge storage capacity, chemical stability, good insulating properties and excellent optical transparency in the visible region. It has a similar band structure as ZnO but a higher dielectric constant (~104), which can favor charge transfer and thus be used as electron transport layer in PSCs. Here, we report on the inverted PSCs with pure SrTiO3 films as cathode buffer layer for the first time. Uniform SrTiO3 films were fabricated on ITO substrate via the PAD method to work as cathode buffer layer in the inverted PSCs. The results indicate that the power conversion efficiency of the solar cells based on P3HT and PCBM with SrTiO3 film as cathode buffer layer and MoO3 as anode interfacial layer is up to 3.5%, comparable to that of PSCs with ZnO as buffer layer reported previously.